Method and apparatus for protecting and transmitting the side information related to peak-to-average power ratio reduction in a multicarrier system

ABSTRACT

A low-complexity and low-latency method and apparatus in multicarrier communication systems is used for protection and transmission of the side information related to peak-to-average power ratio (PAPR) reduction. The side information is encoded by an error-correction code and transmitted through a plurality of reserved sub-carriers. Modulation of the coded side information over the reserved sub-carriers is performed separately without re-performing data modulation. Therefore, the invention dramatically reduces implementation complexity. Determination of the related parameters for PAPR reduction can be based on the PAPR level of data modulated signal with slight degradation in PAPR reduction performance or that of transmitted signal with no degradation in PAPR reduction performance.

FIELD OF THE INVENTION

[0001] The present invention generally relates to the field ofpeak-to-average power ratio (PAPR) reduction in multicarriercommunication systems, such as discrete multitone (DMT) and orthogonalfrequency division multiplexing (OFDM) communication systems, and moreparticularly to a method and apparatus for protection and transmissionof the side information related to PAPR reduction in multicarriercommunication systems.

BACKGROUND OF THE INVENTION

[0002] Multicarrier communication systems, including the most commonlyused DMT and OFDM communication systems, have attracted considerableattention in a variety of high-speed communication applications,including digital subscriber line (DSL), digital terrestrialbroadcasting, wireless local area network (WLAN), wireless metropolitanarea network (WMAN), dedicated short range communication (DSRC), powerline communication, and so on. They also show promise as futuregeneration of mobile communication systems. The advantage ofmulticarrier communication systems comes from dividing high-speed datastream into multiple parallel portions of data streams transmitted viaindividual sub-carriers. Each portion of data stream is transmitted at alower speed and thus robust against the effects of channel impairmentssuch as multipath fading and impulse noise.

[0003]FIG. 1 is a simplified block diagram illustrating a typical OFDMtransmitter. As can be seen from the OFDM transmitter, data X[k], k=0,1, . . . , N−1, to be transmitted within an OFDM symbol period, aretransformed via a serial/parallel (S/P) converter 10, an N-point inversefast Fourier transform (N-IFFT) 20, and a parallel/serial (P/S)converter 30 into the following baseband transmitted signal:$\begin{matrix}\begin{matrix}{{{x\lbrack n\rbrack} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}{{X\lbrack k\rbrack}W_{N}^{kn}}}}},} & {{n = 0},1,\ldots \quad,{N - 1}}\end{matrix} & (1)\end{matrix}$

[0004] where

W _(N) =e ^(j2π/N)  (2)

[0005] is the twiddle factor. The discrete-time transmitted signal x[n]given by (1) is then inserted with cyclic prefix followed bydigital-to-analog (D/A) conversion, and the resultant analog signal x(t)is sent to RF front end for further processing includingin-phase/quadrature-phase (I/Q) modulation, up conversion and poweramplification.

[0006] It is known that the PAPR of the analog signal x(t) is higherthan that of the discrete-time counterpart x[n] by several dB, and canbe approximated by that of x[n/R] where x[n/R] denotes the signal takenfrom R times oversampling of x[n]. Note that the cyclic prefix insertion40 has no any effect on the PAPR level of x(t). Thus, it is convenientto evaluate the PAPR level of x(t) in terms of that of x[n/R] given by$\begin{matrix}{{PAPR} = \frac{\max\limits_{0 \leq n \leq {{RN} - 1}}{{x\left\lbrack {n/R} \right\rbrack}}^{2}}{E\left\{ {{x\left\lbrack {n/R} \right\rbrack}}^{2} \right\}}} & (3)\end{matrix}$

[0007] where E{ } denotes expectation operation. Typically, theapproximation is quite accurate for R≧4.

[0008] One major drawback of multicarrier communication systems is thehigh PAPR of the baseband transmitted signal x(t). When passing throughan RF front end without sufficient power back-offs, the signal x(t) willbe distorted by the nonlinearity of RF power amplifier. In particular,the nonlinearity will incur not only the in-band signal distortionleading to bit-error-rate (BER) performance degradation, but also theout-of-band radiation (or spectrum re-growth) leading to adjacentchannel interference and violation of government's spectrum regulation.

[0009] Conventional solution to this problem is simply utilizing a poweramplifier with large linear range and large power back-offs at theexpense of low power efficiency, high power consumption, and highmanufacturing cost. Alternatively, the problem can be resolved by usingPAPR reduction approaches. One of the PAPR reduction approaches isblock-coding approach, which tries to find out a coding rule so that allthe encoded codewords result in very low PAPR levels for the transmittedsignal x(t). However, extremely low code rate and extraordinaryencoding/decoding complexity make the approach only suitable for systemswith small constellation size and small number of sub-carriers.

[0010] Another PAPR reduction approach is deliberately clippingapproach. In this approach, those amplitude levels of the transmittedsignal exceeding a certain threshold are clipped, and the clipped signalis filtered to eliminate out-of-band radiation. Nevertheless, largeclipping distortion may lead to severe BER performance degradation andinadequately filtering may lead to peak re-growth. On the other hand,probabilistic approach tries to reduce the probability of high PAPRlevel for the transmitted signal by changing the phase, order, level orother properties of the data stream. Probabilistic approach includespartial transmit sequence (PTS) method, selective mapping (SLM) method,tone reservation (TR) method, tone injection (TI) method, and pulsesuperposition method, among which the PTS method seems to be mostattractive in terms of implementation complexity as well as PAPRreduction performance.

[0011] For a number of PAPR reduction methods such as the PTS, SLM andpulse superposition methods, the associated receiver needs to know aboutthe modifications (e.g., the modified phases, orders or levels) thathave been made to the data stream at the transmitter during PAPRreduction procedure. The modifications are referred to as the sideinformation, which is used for correctly recovering the original datastream at the receiver. Correspondingly, the reliability of transmittingthe side information related to PAPR reduction is extremely importantfor system's functionality.

[0012]FIG. 2 is the block diagram of an OFDM transmitter using the PTSmethod, which is disclosed in the U.S. Pat. No. 6,125,103. For reducingthe PAPR of x(t), the input data block X=[X[0], X[1], . . . ,X[N−1]]^(T) is first partitioned into L disjoint sub-blocks (orclusters), denoted by X₁, X₂, . . . , X_(L), of length N where thesuperscript ‘^(T)’ represents vector transposition. Only NIL entries ofX_(l), lε{1, 2, . . . , L}, are taken from the corresponding entries ofX and the remaining ones are set to zero. The partition scheme can beinterleaved, adjacent, or irregular. The L disjoint sub-blocks are thenphase-rotated and combined to form the following signal: $\begin{matrix}{\overset{\sim}{X} = {\sum\limits_{l = 1}^{L}{b_{l}X_{l}}}} & (4)\end{matrix}$

[0013] or, equivalently, $\begin{matrix}\begin{matrix}{{{\overset{\sim}{X}\lbrack k\rbrack} = {\sum\limits_{l = 1}^{L}{b_{l}{X_{l}\lbrack k\rbrack}}}},} & {{k = 0},1,\ldots \quad,{N - 1}}\end{matrix} & (5)\end{matrix}$

[0014] where b_(l) is the phase rotation factor (i.e., |b_(l)|=1)associated with the lth sub-block X_(l).

[0015] Taking N-IFFT of (5) yields the transmitted signal$\begin{matrix}\begin{matrix}{{{\overset{\sim}{x}\lbrack n\rbrack} = {\sum\limits_{l = 1}^{L}{b_{l}{x_{l}\lbrack n\rbrack}}}},} & {{n = 0},1,\ldots \quad,{N - 1}}\end{matrix} & (6)\end{matrix}$

[0016] where x[n], representing the N-IFFT of X_(l)[k], is referred toas the PTS. The goal of the PTS method is to search for optimal phasesequence {b₁, b₂, . . . , b_(L)} such that the PAPR level of theresultant transmitted signal is minimum. In practice, the phase of b_(l)is admitted to be one of a limited set of discrete values {2πm/M, m=0,1, . . . , M−1}, and b₁ can be fixed to unity without sacrificing anyPAPR reduction performance. As such, finding optimal phase sequence {b₂,b₃, . . . , b_(L)} requires performing M^((L−1)) computations of (3),implying that optimal search for {b₂, b₃, . . . , b_(L)} is almostprohibitive for large L and M. For this reason, there have beenlow-complexity sub-optimal search algorithms, for which {b₂, b₃, . . . ,b_(L)} is selected from a smaller subset of all possible candidates of{b₂, b₃, . . . , b_(L)}. Obviously, sub-optimal search algorithms sufferfrom some degradation in PAPR reduction performance.

[0017] The phase sequence {b₂, b₃, . . . , b_(L)} is considered as theside information to be transmitted to the associated receiver, so thatthe receiver can correctly recover the data stream of sub-blocks X_(l),l=2, 3, . . . , L. In conventional PTS method, the side information istransmitted via (L−1) reserved sub-carriers where one sub-carrier withineach sub-block X_(l) (lε{2, 3, . . . , L}) is allocated. Theconventional method, however, provides no protection capability for theside information over these reserved sub-carriers and, thus, may resultin unreliable side information detection at the receiver under noisychannel conditions. On the other hand, our invention provides alow-complexity and low-latency method and apparatus for reliablytransmitting the side information regarding PAPR reduction inmulticarrier communication systems.

SUMMARY OF THE INVENTION

[0018] The present invention has been made to overcome theabove-mentioned drawback of conventional transmission of the sideinformation related to PAPR reduction in multicarrier communicationsystems. An object of the present invention is to provide alow-complexity and low-latency method and apparatus, whereby the sideinformation regarding PAPR reduction in the systems is reliablytransmitted. In particular, the side information is encoded by anerror-correction code and transmitted through a plurality of reservedsub-carriers. Modulation of the coded side information over the reservedsub-carriers is performed separately without re-performing datamodulation. This invention thereby provides the advantages ofdramatically reduced implementation complexity. Moreover, the proposedmethod is applicable to multicarrier communication systems with anynumber of sub-carriers and any type of data constellation, whileintroducing only slight or no degradation in PAPR reduction performance.

[0019] According to the invention, determination of the relatedparameters for PAPR reduction can be based on the PAPR of data modulatedsignal with slight degradation in PAPR reduction performance.Alternatively, it can also be based on the PAPR of transmitted signalwith no loss of PAPR reduction performance.

[0020] The foregoing and other objects, features, aspects and advantagesof the present invention will become better understood from a carefulreading of the detailed description provided herein below withappropriate reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention can be understood in more detail by readingthe subsequent detailed description in conjunction with the examples andreferences made to the accompanying drawings, wherein:

[0022]FIG. 1 is a simplified block diagram illustrating a typical OFDMtransmitter;

[0023]FIG. 2 is the block diagram of a conventional OFDM transmitterusing the PTS method;

[0024]FIG. 3 is the block diagram of an OFDM transmitter illustratingthe first embodiment of the present invention;

[0025]FIG. 4 is the block diagram of an OFDM transmitter illustratinganother embodiment of the present invention;

[0026]FIG. 5 is a more detailed block diagram illustrating the OFDMmodulator, the parameter control device for PAPR reduction, and the sideinformation coding and modulation device shown in FIG. 3, in which thePTS method is used and K reserved sub-carriers are used for protectingand transmitting the side information;

[0027]FIG. 6 illustrates the allocation of the K reserved sub-carriersfor the OFDM transmitter shown in FIG. 5;

[0028]FIG. 7 is the block diagram of an OFDM receiver for detecting anddecoding the transmitted side information as well as for recovering theoriginal data stream;

[0029]FIG. 8 are exemplary diagrams of computing the partial N-IFFT for(a) any given frequency p₁ and (b) a certain frequency p₁=N/8, and (c)an exemplary diagram of constructing the look-up mapping table in amemory device to generate a period of the side information modulatedsignal {tilde over (x)}S[n] for p₁=N/8;

[0030]FIG. 9 is a more detailed block diagram illustrating the OFDMmodulator, the parameter control device for PAPR reduction, and the sideinformation coding and modulation device shown in FIG. 4, in which thePTS method is used and K reserved sub-carriers are used for protectingand transmitting the side information;

[0031]FIG. 10 is a more detailed block diagram illustrating the OFDMmodulator, the parameter control device for PAPR reduction, and the sideinformation coding and modulation device shown in FIG. 3, in which thePTS method is used and two groups of reserved sub-carriers are used forprotecting and transmitting the side information;

[0032]FIG. 11 illustrates the allocation of the two groups of reservedsub-carriers for the OFDM transmitter in FIG. 10;

[0033]FIG. 12 is a more detailed block diagram illustrating the OFDMmodulator, the parameter control device for PAPR reduction, and the sideinformation coding and modulation device shown in FIG. 4, in which thePTS method is used and two groups of reserved sub-carriers are used forprotecting and transmitting the side information;

[0034] FIGS. 13(a) and 13(b) plot the complementary cumulativedistribution function of the obtained 10⁵ independent realizations ofPAPR levels for 128 and 1024 sub-carriers, respectively; and

[0035] FIGS. 14(a) and 14(b) plot the word-error-rate performance of the‘word’ {b₂, b₃, b₄} for the frequency flat and frequency selectivechannels, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036]FIG. 3 is the block diagram of an OFDM transmitter in accordancewith the first embodiment of the present invention. Referring to FIG. 3,the data X[k], k=0, 1, . . . , N−1, to be transmitted within an OFDMsymbol period, are transformed via a S/P converter 10 into the inputdata block X. The OFDM modulator 100 having a parameter control device200 for PAPR reduction performs OFDM modulation of the input data X andgenerates the data modulated signal {tilde over (x)}_(D). The parametercontrol device 200 sequentially selects a set of parameters from allpossible sets of parameters for PAPR reduction, and sends each set ofselected PAPR reduction parameters to the OFDM modulator 100. The OFDMmodulator 100 further modulates the input data X in accordance with thePAPR reduction parameters and derives the corresponding data modulatedsignal {tilde over (x)}_(D). The procedure of selecting a new set ofPAPR reduction parameters and deriving the corresponding data modulatedsignal {tilde over (x)}_(D) is repeated until an acceptable PAPR levelof {tilde over (x)}_(D) is achieved. Alternately, it is repeated untilall possible sets of PAPR reduction parameters have been selected andall the PAPR levels of the corresponding {tilde over (x)}_(D) have beencomputed. Then, a set of optimal (or sub-optimal) PAPR reductionparameters is determined according to the computed PAPR levels of {tildeover (x)}_(D).

[0037] After the set of optimal (or sub-optimal) PAPR reductionparameters has been determined, the side information coding andmodulation device 300 performs encoding and OFDM modulation for therelated information of the optimal (or sub-optimal) PAPR reductionparameters, referred to as the side information, and derives the sideinformation modulated signal {tilde over (x)}_(S). The side informationmodulated signal {tilde over (x)}_(S) and the data modulated signal{tilde over (x)}_(D) are further combined via an adder 400 to yield thetransmitted signal {tilde over (x)}, which is then transformed into thetransmitted sequence {tilde over (x)}[n] via a P/S converter 30. Notethat adding the side information modulated signal {tilde over (x)}_(S)to the data modulated signal {tilde over (x)}_(D) may lead to theresultant transmitted signal {tilde over (x)} with a slightly higherPAPR level than that of {tilde over (x)}_(D) Because the PAPR reductionparameters are determined based on the data modulated signal {tilde over(x)}_(D), a slight degradation in PAPR reduction performance could beintroduced.

[0038] In the first embodiment of FIG. 3, several sub-carriers arereserved for transmitting the side information, while the rest ofsub-carriers are used for data transmission. The side informationaccording to the embodiment of the invention can thus be properlyprotected. Moreover, modulation of the coded side information over thereserved sub-carriers and modulation of the data over the rest ofsub-carriers are performed separately, thereby providing the benefit ofdramatically reduced implementation complexity.

[0039]FIG. 4 is the block diagram of an OFDM transmitter in accordancewith another embodiment of the present invention. The data X[k], k=0, 1,. . . , N−1, to be transmitted within an OFDM symbol period, aretransformed via a S/P converter 10 into the input data block X. The OFDMmodulator 100 having a parameter control device 200 for PAPR reductionperforms OFDM modulation of the input data X and generates the datamodulated signal {tilde over (x)}_(D). Similar to the embodiment of FIG.3, several sub-carriers are reserved for transmitting the sideinformation. In the embodiment of FIG. 4, how to yield the transmittedsequence {tilde over (x)}[n] will become better understood from thedetailed description provided herein below with reference to FIG. 4.

[0040] Referring to FIG. 4, during the procedure of determining optimal(or sub-optimal) PAPR reduction parameters, the parameter control device200 sends each set of selected PAPR reduction parameters to the OFDMmodulator 100. The OFDM modulator 100 modulates the input data X inaccordance with these PAPR reduction parameters and derives thecorresponding data modulated signal {tilde over (x)}_(D). At the sametime, the side information coding and modulation device 300 performsencoding and OFDM modulation for the related information of the selectedPAPR reduction parameters, referred to as the side information, andderives the side information modulated signal {tilde over (x)}_(S). Theside information modulated signal {tilde over (x)}_(S) and the datamodulated signal {tilde over (x)}_(D) are further combined via an adder400 to yield the transmitted signal {tilde over (x)}. The procedure ofselecting a new set of PAPR reduction parameters and deriving thecorresponding transmitted signal {tilde over (x)} is repeated until anacceptable PAPR level of {tilde over (x)} is achieved. Alternatively, itis repeated until all possible sets of PAPR reduction parameters havebeen selected and all the PAPR levels of the corresponding {tilde over(x)} have been computed. Then, a set of optimal (or sub-optimal) PAPRreduction parameters is determined according to the computed PAPR levelsof {tilde over (x)}. After the PAPR reduction procedure has beencompleted, the finally resultant transmitted signal {tilde over (x)} istransformed into the transmitted sequence {tilde over (x)}[n] via a P/Sconverter 30.

[0041] The thereby obtained optimal (or sub-optimal) PAPR reductionparameters always reflect the PAPR level of the finally resultanttransmitted sequence {tilde over (x)}[n]. Thus, the embodiment of FIG. 4can protect the side information without any degradation of PAPRreduction performance, while introducing only slightly increasedcomputation complexity.

[0042] In the following, for clear and simple presentation, the presentinvention is further illuminated in terms of only the PTS method,although it can also be applied to other types of PAPR reductionmethods.

[0043]FIG. 5 is a more detailed block diagram illustrating the OFDMmodulator 100, the parameter control device 200 for PAPR reduction, andthe side information coding and modulation device 300 shown in FIG. 3.In FIG. 5, the parameter control device 200 determines an optimal (orsub-optimal) phase sequence {b₂, b₃, . . . , b_(L)} according to thePAPR level of the data modulated signal XD from the OFDM modulator 100.As mentioned before, when the PTS method searches for optimal (orsub-optimal) phase sequence {b₁, b₂, . . . , b_(L)}, the phase of b₁ isadmitted to be one of a limited set of discrete values {2πm/M, m=0, 1, .. . , M−1}, and b₁ can be fixed to unity without sacrificing any PAPRreduction performance.

[0044] In the following, how to protect and transmit the sideinformation about the phase sequence {b₂, b₃, . . . , b_(L)} via Kreserved sub-carriers is further described.

[0045] In order to easily encode the phase sequence {b₂, b₃, . . . ,b_(L)}, the present invention first establishes a one-by-one mappingbetween each of the possibly used {b₂, b₃, . . . , b_(L)} and acorresponding index i, where iε{0, 1, . . . , I−1} and I denotes thenumber of the possible candidates of {b₂, b₃, . . . , b_(L)}. Note thatI=M^((L−1)) for optimal search algorithms and may be less than M^((L−1))for suboptimal search algorithms. Table 1 shows an example of suchmapping with L=4 (four sub-blocks) and M=2 (b_(l)ε{±11}) for optimalsearch algorithms (I=2³=8). TABLE 1 An exemplary mapping table foroptimal search algorithms (L = 4, M = 2 and I = 8) Index i Binaryrepresentation b₂ b₃ b₄ 0 000 1 1 1 1 001 1 1 −1 2 010 1 −1 1 3 011 1 −1−1 4 100 −1 1 1 5 101 −1 1 −1 6 110 −1 −1 1 7 111 −1 −1 −1

[0046] In FIG. 5, the parameter control device 200 for PAPR reductionfurther comprises a phase optimization unit 60 and a phase mapper 70.The phase optimization unit 60 sequentially selects an index i from theset of {1, 2, . . . , I} and the phase mapper 70 generates theassociated phase sequence {b₂, b₃, . . . , b_(L)} according to themapping as illustrated in Table 1, so that the OFDM modulator 100 canderive a new data modulated signal {tilde over (x)}_(D). Such step isrepeated until an optimal (or sub-optimal) phase sequence {b₂, b₃, . . ., b_(L)} is found.

[0047] Let is denote the index i corresponding to the determined {b₂,b₃, . . . , b_(L)} after phase optimization, then knowing the indexi_(S) is equivalent to knowing the determined sequence {b₂, b₃, . . . ,b_(L)}. Thus, the side information about {b₂, b₃, . . . , b_(L)} can besimply protected by error-correction encoding of the index i_(S).

[0048] Further referring to FIG. 5, after the phase optimization unit 60has determined the optimal (or sub-optimal) index is, the index i_(S) isfed to the side information coding and modulation device 300 to generatethe side information modulated signal {tilde over (x)}_(S). The sideinformation coding and modulation device 300 uses an error-correctioncode to protect the side information (the index i_(S)), and performsOFDM modulation of the coded side information. Specifically, the sideinformation coding and modulation device 300 comprises an encoder 310 toproceed error-correction encoding of the index i_(S), and the resultantcodeword is mapped into a sequence {d₁, d₂, . . . , d_(K)} of K symbolsvia a symbol mapper 320. The sequence {d₁, d₂, . . . , d_(K)} is thenmodulated onto K reserved sub-carriers {p₁, p₂, . . . , p_(K)} by meansof N-IFFT.

[0049] In general, the number of reserved sub-carriers is very few inthe embodiment of FIG. 5. This allows the embodiment of FIG. 5 tosimplify the required operations for N-IFFT as a partial N-IFFT 330 withdifferent degree of complexity according to different arrangement of thereserved sub-carriers {p₁, p₂, . . . , p_(K)}. The simplified processwill be described later.

[0050]FIG. 6 illustrates the allocation of the K reserved sub-carriersfor the OFDM transmitter in FIG. 5, in which the reserved sub-carriersare used for transmitting the coded side information. The data modulatedsignal {tilde over (x)}_(D) and the side information modulated signal{tilde over (x)}_(S) are corresponding to the N-IFFTs of the followingsignals, respectively: $\begin{matrix}\begin{matrix}{{{{\overset{\sim}{X}}_{D}\lbrack k\rbrack} = {\sum\limits_{l = 1}^{L}{b_{l}{X_{l}\lbrack k\rbrack}}}},} & {{k = 0},1,\ldots \quad,{N - 1},}\end{matrix} & (7) \\{and} & \quad \\{{{\overset{\sim}{X}}_{s}\lbrack k\rbrack} = \left\{ \begin{matrix}{d_{m},} & {{{{for}\quad k} = p_{m}},{m = 1},2,\ldots \quad,K} \\{0,} & {otherwise}\end{matrix} \right.} & (8)\end{matrix}$

[0051] where

X _(l) [k]=0, for k=p _(m), m=1, 2, . . . , K  (9)

[0052] are reserved for transmitting the coded side information. Theadder 400 in FIG. 5 sums up {tilde over (x)}_(D) and {tilde over(x)}_(S), and generates the transmitted sequence

{tilde over (x)}[n]={tilde over (x)} _(D) [n]+{tilde over (x)} _(S) [n],n=0, 1, . . . , N−1. (10)

[0053] Further referring to both FIG. 5 and FIG. 6 and according to (7)to (9), taking N-IFFT of (10) yields $\begin{matrix}{{\overset{\sim}{X}\lbrack k\rbrack} = {{{{\overset{\sim}{X}}_{D}\lbrack k\rbrack} + {{\overset{\sim}{X}}_{S}\lbrack k\rbrack}} = \left\{ {\begin{matrix}{d_{m},} & {{{{if}\quad k} = p_{m}},{m = 1},2,\ldots \quad,K} \\{{{\overset{\sim}{X}}_{D}\lbrack k\rbrack},} & {otherwise}\end{matrix}.} \right.}} & (11)\end{matrix}$

[0054] Accordingly, an OFDM receiver for recovering both the sideinformation and the original data is illustrated in FIG. 7. Referring toFIG. 7, the OFDM receiver receives the sequence y[n], which istransformed into the data block y via a S/P converter 10. After thereceived data y have been proceeded through an N-point fast Fouriertransform (N-FFT) 550 and an equalizer 540, K symbols on the reservedsub-carriers {p₁, p₂, . . . , p_(K)} are picked out. Then, from the Ksymbols, the side information demodulation and decoding device 500 findsout the phase sequence {{circumflex over (b)}₂*, {circumflex over(b)}₃*, . . . , {circumflex over (b)}_(L)*} that has been determined atthe transmitter. According to the obtained phase sequence {{circumflexover (b)}₂*, {circumflex over (b)}₃*, . . . , {circumflex over(b)}_(L)*}, the OFDM receiver removes the phase rotations made at thetransmitter and recovers the data sequence {circumflex over (X)}[k].

[0055] As can be seen from FIG. 7, the side information demodulation anddecoding device 500 further comprises a symbol de-mapper 510, a decoder520 and a phase mapper 530 for finding out the phase sequence determinedat the transmitter. The symbol de-mapper 510 de-maps the K symbols onthe sub-carriers {p₁, p₂, . . . , p_(K)} into a corresponding codeword,and the decoder 520 decodes this codeword into a corresponding indexî_(S). The phase mapper 530 then transforms the index î_(S) into acorresponding phase sequence {{circumflex over (b)}₂*, {circumflex over(b)}₃*, . . . , {circumflex over (b)}_(L)*}.

[0056] Further referring to FIG. 5, the complexity for deriving the sideinformation modulated signal {circumflex over (x)}_(S) or, equivalently,for computing the N-IFFT of {circumflex over (X)}_(S)[k] can bedramatically reduced by virtue of the periodic property of the twiddlefactor W_(N) as well as the fact that the number of reservedsub-carriers is very few in general. This is explained by consideringthe following case. The input data block X is divided into foursub-blocks (L=4), and the coded side information is mapped into thesequence {d₁, d₂, d₃, d₄} (K=4) which is to be transmitted throughsub-carriers {p₁, p₂, p₃, p₄}={p₁, p₁+N/4, p₁+2N/4, p₁+3N/4}.

[0057] Then, it can be easily shown that the side information modulatedsignal $\begin{matrix}\begin{matrix}{{{\overset{\sim}{x}}_{S}\lbrack n\rbrack} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}{{{\overset{\sim}{X}}_{S}\lbrack k\rbrack}W_{N}^{kn}}}}} \\{{= {{W_{N}^{{np}_{1}} \cdot \frac{1}{\sqrt{N}}}{\sum\limits_{m = 0}^{3}{d_{m + 1}W_{4}^{mn}}}}},{n = 0},1,\ldots \quad,{N - 1}}\end{matrix} & (12)\end{matrix}$

[0058] This reveals that the N-IFFT of {tilde over (X)}_(S)[k] can besimply implemented by a 4-IFFT followed by (N−1) complex multipliers(associated with W_(N) ^(np) ^(₂) ), as shown in FIG. 8(a).

[0059] When p₁=N/8, the implementation in FIG. 8(a) reduces to the onein FIG. 8(b) where only a 4-IFFT and four complex multipliers areneeded. Furthermore, only a 4-IFFT is needed for p₁=0. Note that theoriginal N-IFFT requires Nlog₂N complex additions and (N/2)log₂N complexmultiplication operations, whereas the simplified implementation,referred to as the partial N-IFFT 330 for clarity, requires only eightcomplex additions and (N+3) complex multiplication operations for anygiven frequency p₁. On the other hand, generation of the sideinformation modulated signal {tilde over (x)}_(S)[n] depends only on thegiven index i implying that {tilde over (x)}_(S)[n] can be generated bysimply looking through a mapping table that has been constructed inadvance for all iε{0, 1, . . . , I−1} and can be stored in a memorydevice such as a read-only memory (ROM). Similarly, the size of themapping table (the memory device) can be reduced dramatically by virtueof the above-mentioned fact and the periodic property of the twiddlefactor, as exemplified in FIG. 8(c) for p₁=N/8.

[0060] Note that in the embodiment of FIG. 5, determination of the indexi_(S) is based on the PAPR level of the data modulated signal {tildeover (x)}_(D), implying that adding the side information modulatedsignal {tilde over (x)}_(S) to the signal {tilde over (x)}_(D) as givenby (10) may lead to an increased PAPR level of the transmitted signal{tilde over (x)}_(S). The resultant degradation of PAPR reductionperformance, however, can be negligible if the total power of {tildeover (x)}_(S) is much less than that of {tilde over (x)}_(D).

[0061] Alternatively, another embodiment as shown in FIG. 9 of thepresent invention determines the index is based on the PAPR level of thetransmitted signal x without any degradation of PAPR reductionperformance. FIG. 9 is a more detailed block diagram of the OFDMtransmitter shown in FIG. 4, in which the parameter control device 200for PAPR reduction and the side information coding and modulation device300 are further illustrated. The side information coding and modulationdevice 300 generates the side information modulated signal {tilde over(x)}_(S) for every selected index iε{0, 1, . . . , I−1} during phaseoptimization, and thus the embodiment of FIG. 9 requires morecomputations than that of FIG. 5.

[0062] Next, other embodiments of the present invention with furtherreduced complexity are provided. First, the invention divides thesequence {d₁, d₂, . . . , d_(K)} regarding the coded side informationinto two sequences, {d₁, d₂, . . . , d_({tilde over (K)})} and {{squareroot}{square root over (P_(b))}b₂, {square root}{square root over(P_(b))}b₃, . . . , {square root}{square root over (P_(b))}b_(L)}, where{tilde over (K)}+(L−1)=K and P_(b) is the average power for transmittingthe latter sequence. The former sequence {d₁, d₂, . . . ,d_({tilde over (K)})} is to be modulated onto {tilde over (K)} reservedsub-carriers {p₁, p₂, . . . , p_({tilde over (K)})} for transmittingpart of the coded side information, while the latter sequence {{squareroot}{square root over (P_(b))}b₂, {square root}{square root over(P_(b))}b₃, . . . , {square root}{square root over (P_(b))}b_(L)} is tobe imposed onto (L−1) reserved sub-carriers {q₂, q₃, . . . , q_(L)} fortransmitting the remaining part of the coded side information.

[0063]FIG. 10 is a more detailed block diagram illustrating the OFDMtransmitter shown in FIG. 3, in which the PTS method is used and theparameter control device 200 for PAPR reduction and the side informationcoding and modulation device 300 are further illustrated. Referring toFIG. 10, the parameter control device 200 for PAPR reduction comprises aphase optimization unit 60 and a phase mapper 70. The phase mapper 70 isimplemented by an encoder 72 followed by an M-ary phase-shift keying(PSK) mapper 71. For optimal search algorithms, the encoder 72 isinexistent and the phase mapper 70 reduces to the M-ary PSK mapper 71,which is illustrated again as in Table 1 with binary bits {0, 1} mappedinto BPSK symbols {+1, −1}, respectively. The BPSK symbols from theM-ary PSK mapper 71 (M=2) are then used as the phase rotation factorsb_(l), l=2, 3, . . . , L.

[0064] For sub-optimal algorithms, Table 2 shows another example of suchphase mapping with L=4 (four sub-blocks) and M=4 (b_(l)ε{±1, ±j}), whereonly I (=8) candidates of {b₂, b₃, b₄} out of total 64 (=4³) candidatesare used for selecting sub-optimal phase sequence {b₂, b₃, b₄}. Theindex i in Table 2 is encoded by the encoder 72 with a linear (6, 3)block code of generator matrix $\begin{matrix}{G = \begin{bmatrix}0 & 1 & 1 & 1 & 0 & 0 \\1 & 0 & 1 & 0 & 1 & 0 \\1 & 1 & 0 & 0 & 0 & 1\end{bmatrix}} & (13)\end{matrix}$

[0065] and two-tuple binary bits {00, 01, 11, 10} in the resultantcodeword are mapped into quarternary phase shift keying (QPSK) symbols{1, j, −1, −j}, respectively. The QPSK symbols from the M-ary PSK mapper71 (M=4) are then used as the phase rotation factors b_(l), l=2, 3, . .. , L. TABLE 2 An exemplary mapping table for sub-optimal searchalgorithms (L = 4, M = 4 and I = 8) Index Binary i representationcodeword b₂ b₃ b₄ 0 000 00 00 00 1 1 1 1 001 11 00 01 −1 1 j 2 010 10 1010 −j −j −j 3 011 01 10 11 j −j −1 4 100 01 11 00 j −1 1 5 101 10 11 01−j −1 j 6 110 11 01 10 −1 j −j 7 111 00 01 11 1 j −1

[0066] As shown in FIG. 10, two-stage encoding of the index is isprovided to protect the side information. During phase optimization, thefirst-stage encoding of each index i is performed by the encoder 72 andthe resultant codeword is mapped to the sequence {b₂, b₃, . . . , b_(L)}by the M-ary PSK mapper 71. By allocating one sub-carrier per sub-blockwith the value of {square root}{square root over (P_(b))}, the sequence{{square root}{square root over (P_(b))}b₂, {square root}{square rootover (P_(b))}b₃, . . . , {square root}{square root over (P_(b))}b_(L)}for index i can be imposed onto the (L−1) reserved sub-carriers {q₂, q₃,. . . , q_(L)}, where sub-carrier q_(l) is within the frequency range ofthe lth sub-block. After phase optimization, the codeword for the indexis from the encoder 72 is fed to the side information coding andmodulation device 300 for second-stage encoding and modulation. The sideinformation coding and modulation device 300 comprises a parity-bitgenerator 315, a symbol mapper 320 for mapping the generated parity bitsinto the sequence {d₁, d₂, . . . , d_({tilde over (K)})}, and a partialN-IFFT 330 for performing OFDM modulation of the sequence {d₁, d₂, . . ., d_({tilde over (K)})} according to the arrangement of sub-carriers{p₁, p₂, . . . , p_({tilde over (K)})}.

[0067]FIG. 11 shows an example illustrating the allocation of the twogroups of reserved sub-carriers {p₁, p₂, . . . , p_({tilde over (K)})}and {q₂, q₃, . . . , q_(L)} for two-stage protection of the sideinformation. Let the N-FFT of the data modulated signal {tilde over(x)}_(D)[n] be given as (7) with $\begin{matrix}{{X_{l}\lbrack k\rbrack} = \left\{ \begin{matrix}{0,} & {{{{for}\quad k} = p_{m}},{m = 1},2,\ldots \quad,\overset{\sim}{K}} \\{\sqrt{P_{b}},} & {{{{for}\quad k} = q_{l}},{l = 2},3,\ldots \quad,L}\end{matrix} \right.} & (14)\end{matrix}$

[0068] and the N-FF1 of the side information modulated signal {tildeover (x)}_(S)[n] be given as $\begin{matrix}{{{\overset{\sim}{X}}_{S}\lbrack k\rbrack} = \left\{ \begin{matrix}{d_{m},} & {{{{for}\quad k} = p_{m}},{m = 1},2,{\ldots \quad \overset{\sim}{K}}} \\{0,} & {otherwise}\end{matrix} \right.} & (15)\end{matrix}$

[0069] It can be easily seen, from (7), (10), (14) and (15), that$\begin{matrix}{{\overset{\sim}{X}\lbrack k\rbrack} = {{{{\overset{\sim}{X}}_{D}\lbrack k\rbrack} + {{\overset{\sim}{X}}_{S}\lbrack k\rbrack}} = \left\{ \begin{matrix}{d_{m},} & {{{{for}\quad k} = p_{m}},{m = 1},2,\ldots \quad,\overset{\sim}{K}} \\{{\sqrt{P_{b}} \cdot b_{l}},} & {{{{for}\quad k} = q_{l}},{l = 2},3,\ldots \quad,L} \\{{{\overset{\sim}{X}}_{D}\lbrack k\rbrack},} & {otherwise}\end{matrix} \right.}} & (16)\end{matrix}$

[0070] This reveals that with the allocation as in FIG. 11, the twosequences {d₁, d₂, . . . , d_({tilde over (K)})} and {{squareroot}{square root over (P_(b))}b₂, {square root}{square root over(P_(b))}b₃, . . . , {square root}{square root over (P_(b))}b_(L)}representing the two-stage coded side information are put on two groupsof reserved sub-carriers {p₁, p₂, . . . , p_({tilde over (K)})} and {q₂,q₃, . . . , q_(L)}, respectively. Therefore, the resultant transmittedsignal {tilde over (x)}[n] contains both groups of symbols fortransmission of the index is. The corresponding receiver is similar tothat in FIG. 7.

[0071] Because of the fact that {tilde over (K)}<K, the embodiment ofFIG. 10 has the benefits of lower complexity for computing the partialN-IFFT of {tilde over (X)}_(S)[k] and less degradation in PAPR reductionperformance than that of FIG. 5, where both embodiments determining theindex i_(S) are based on the PAPR level of the data modulated signal{tilde over (x)}_(D).

[0072] Similarly, obtaining the index i during phase optimization canalso be based on the PAPR level of the transmitted signal {tilde over(x)} as illustrated by the embodiment of FIG. 12, thereby furtherreducing complexity in FIG. 9. FIG. 12 is a more detailed block diagramillustrating the OFDM transmitter shown in FIG. 4, in which the PTSmethod is used and the parameter control device 200 for PAPR reductionand the side information coding and modulation device 300 are furtherillustrated. The parameter control device 200 for PAPR reductioncomprises a phase optimization unit 60 and a phase mapper 70. The phasemapper 70 is implemented by an encoder 72 followed by an M-ary PSKmapper 71. The PSK sequence {b₂, b₃, . . . , b_(L)} from the M-ary PSKmapper 71 are imposed onto (L−1) reserved sub-carriers {q₂, q₃, . . . ,q_(L)}. The side information coding and modulation device 300 comprisesa parity-bit generator 315 for encoding the output from the encoder 72,and a symbol mapper 320 for mapping the parity bits from the parity-bitgenerator 315 into the sequence {d₁, d₂, . . . , d_({tilde over (K)})},and a partial N-IFFT 330 for performing OFDM modulation of the sequence{d₁, d₂, . . . , d{tilde over (K)}} according to the arrangement ofsub-carriers {p₁, p₂, . . . , p_({tilde over (K)})}. This thereforetransmits the two-stage coded side information through two groups ofreserved sub-carriers {p₁, p₂, . . . , p_({tilde over (K)})} and {q₂,q₃, . . . , q_(L)}. Similar to the embodiment of FIG. 10, transmissionof the index i_(S) is completed through the generation of the twosequences {d₁, d₂, . . . , d_({tilde over (K)})} and {b₂, b₃, . . . ,b_(L)}. The corresponding receiver is also similar to that in FIG. 7.

[0073] In the following, some simulation results regarding theembodiments of FIG. 10 and FIG. 12 for verifying the present inventionare provided.

[0074] In the simulation, the data X[k]'s were assumed to be equallyprobable 16-QAM symbols with unit variance, and the optimal search PTSmethod with adjacent partition scheme was used for L=4 (four sub-blocks)and M=2 (b_(l)ε{±1}). For the embodiments of FIGS. 10 and 12, theencoder 72 was inexistent due to utilization of optimal searchalgorithm, and three information bits representing the index i weremapped into the BPSK sequence {b₂, b₃, b₄} by the M-ary PSK mapper 71with the phase mapping as in Table 1. The three information bits wereencoded by the linear (6, 3) block code given by (13) where theresultant three parity bits as the outputs of the parity-bit generator315 were mapped into the BPSK sequence {d₁, d₂, d₃} (i.e., {tilde over(K)}=3) by the symbol mapper 320. The two sequences {d₁, d₂, d₃} and{b₂, b₃, b₄} ({square root}{square root over (P_(b))}=1) weretransmitted through two groups of reserved sub-carriers {p₁, p₂,p₃}={N/8, 3N/8, 5N/8} and {q₂, q₃, q₄}={2N/8, 4N/8, 6N/8}, respectively.The PAPR reduction performance was evaluated based on four timesoversampling (R=4) of the resultant transmitted signal {tilde over(x)}[n] (using (3)) and 10⁵ Monte Carlo Runs.

[0075] FIGS. 13(a) and 13(b) plot the complementary cumulativedistribution function (CCDF), Pr{PAPR>PAPR₀}, of the obtained 10⁵independent realizations of PAPR levels for 128 and 1024 sub-carriers,respectively. Note that the lines indicated by “ORIGINAL” in thesefigures are the results obtained without any PAPR reduction, and thoseindicated by “PTS” are the ones obtained using the optimal search PTSmethod with no sub-carriers reserving for side information transmission.From FIG. 13(a) (N=128), it can be observed that the embodiment of FIG.10 exhibits a little bit performance degradation in PAPR reductionwhereas that of FIG. 12 slightly improves the PAPR reductionperformance. These performance disparities, however, are almostinvisible in FIG. 13(b) for the case of N=1024.

[0076] On the other hand, the detection performance for {b₂, b₃, b₄} wasevaluated by passing the transmitted signal x[n] (N=1024) through afrequency flat channel as well as a two-path frequency selective channelwhose impulse response h[n]=δ[n]+0.5δ[n−5]. The received signal wasassumed to be corrupted by additive white Gaussian noise (AWGN).

[0077] FIGS. 14(a) and 14(b) plot the word-error-rate (WER) performanceof the ‘word’ {b₂, b₃, b₄} of the present invention (the lines indicatedby “CODED”) for the frequency flat and frequency selective channels,respectively. For comparison, the results obtained using only thesequence {b₂, b₃, b₄} for side information transmission through reservedsub-carriers {q₂, q₃, q₄} (i.e., the conventional PTS method) are alsoplotted (the lines indicated by “UNCODED”). From FIGS. 14(a) and 14(b),it can be seen that the present invention provides about 3 dB and 6 dBcoding gains over the conventional PTS method at WER=10⁻² for thefrequency flat and frequency selective channels, respectively. Theseresults therefore demonstrate the efficacy of the present invention.

[0078] Although the present invention has been described with referenceto the preferred embodiments, it should be understood that the inventionis not limited to the details described thereof. Various substitutionsand modifications have been suggested in the foregoing description, andothers will occur to those of ordinary skill in the art. Therefore, allsuch substitutions and modifications are intended to be embraced withinthe scope of the invention as defined in the appended claims.

What is claimed is:
 1. A method for protecting and transmitting the sideinformation related to peak-to-average power ratio (PAPR) reduction in amulticarrier system, comprising the steps of: (a) performingmulticarrier modulation for the data to be transmitted and generating adata modulated signal, then executing a procedure related to said PAPRreduction; (b) encoding said side information for generating coded sideinformation; (c) allocating a plurality of sub-carriers for transmittingsaid coded side information; (d) performing multicarrier modulation forsaid coded side information and generating a side information modulatedsignal; and (e) attaching said side information modulated signal to saiddata modulated signal for generating a transmitted signal; wherein saidPAPR reduction procedure is based on either the PAPR level of said datamodulated signal or that of said transmitted signal.
 2. The method forprotecting and transmitting the side information related to PAPRreduction in a multicarrier system as claimed in claim 1, wherein saidencoding said side information is implemented through anerror-correction coding procedure.
 3. The method for protecting andtransmitting the side information related to PAPR reduction in amulticarrier system as claimed in claim 1, wherein said PAPR reductionprocedure is based on either the PAPR level of said data modulatedsignal or that of said transmitted signal to determine PAPR reductionparameters.
 4. The method for protecting and transmitting the sideinformation related to PAPR reduction in a multicarrier system asclaimed in claim 3, wherein said PAPR reduction parameters are said sideinformation.
 5. The method for protecting and transmitting the sideinformation related to PAPR reduction in a multicarrier system asclaimed in claim 1, wherein said PAPR reduction procedure is a partialtransmit sequence method.
 6. The method for protecting and transmittingthe side information related to PAPR reduction in a multicarrier systemas claimed in claim 3, wherein said PAPR reduction procedure is based onthe PAPR level of said data modulated signal, and said steps (b), (d),and (e) are performed after said PAPR reduction parameters have beendetermined.
 7. The method for protecting and transmitting the sideinformation related to PAPR reduction in a multicarrier system asclaimed in claim 4, wherein said PAPR reduction procedure is based onthe PAPR level of said data modulated signal, and said steps (b), (d),and (e) are performed after said PAPR reduction parameters have beendetermined.
 8. The method for protecting and transmitting the sideinformation related to PAPR reduction in a multicarrier system asclaimed in claim 3, wherein said PAPR reduction procedure is based onthe PAPR level of said transmitted signal, and said steps (b), (d), and(e) are performed during said PAPR reduction procedure.
 9. The methodfor protecting and transmitting the side information related to PAPRreduction in a multicarrier system as claimed in claim 4, wherein saidPAPR reduction procedure is based on the PAPR level of said transmittedsignal, and said steps (b), (d), and (e) are performed during said PAPRreduction procedure.
 10. A method for protecting and transmitting theside information related to peak-to-average power ratio (PAPR) reductionin a multicarrier system, comprising the steps of: (a) performingmulticarrier modulation for the data to be transmitted and generating adata modulated signal, then executing a procedure related to said PAPRreduction; (b) encoding said side information and generating two groupsof coded side information; (c) allocating two groups of a plurality ofsub-carriers for transmitting said two groups of coded side informationrespectively; (d) combining one of said two groups of coded sideinformation with said data modulated signal; (e) modulating the othergroup of said two groups of coded side information and generating a sideinformation modulated signal; and (f) attaching said side informationmodulated signal to said data modulated signal for generating atransmitted signal; wherein said PAPR reduction procedure is based oneither the PAPR level of said data modulated signal or that of saidtransmitted signal.
 11. The method for protecting and transmitting theside information related to PAPR reduction in a multicarrier system asclaimed in claim 10, wherein said said step (b) is implemented throughan error-correction coding procedure and a parity-bit generationprocedure.
 12. The method for protecting and transmitting the sideinformation related to PAPR reduction in a multicarrier system asclaimed in claim 10, wherein said PAPR reduction procedure is based oneither the PAPR level of said data modulated signal or that of saidtransmitted signal to determine PAPR reduction parameters.
 13. Themethod for protecting and transmitting the side information related toPAPR reduction in a multicarrier system as claimed in claim 12, whereinsaid PAPR reduction parameters are said side information.
 14. The methodfor protecting and transmitting the side information related to PAPRreduction in a multicarrier system as claimed in claim 10, wherein saidPAPR reduction procedure is a partial transmit sequence method.
 15. Themethod for protecting and transmitting the side information related toPAPR reduction in a multicarrier system as claimed in claim 12, whereinsaid PAPR reduction procedure is based on the PAPR level of said datamodulated signal, and said steps (b), (e), and (f) are performed aftersaid PAPR reduction parameters have been determined.
 16. The method forprotecting and transmitting the side information related to PAPRreduction in a multicarrier system as claimed in claim 13, wherein saidPAPR reduction procedure is based on the PAPR level of said datamodulated signal, and said steps (b), (e), and (f) are performed aftersaid PAPR reduction parameters have been determined.
 17. The method forprotecting and transmitting the side information related to PAPRreduction in a multicarrier system as claimed in claim 12, wherein saidPAPR reduction procedure is based on the PAPR level of said transmittedsignal, and said steps (b), (e), and (f) are performed during said PAPRreduction procedure.
 18. The method for protecting and transmitting theside information related to PAPR reduction in a multicarrier system asclaimed in claim 13, wherein said PAPR reduction procedure is based onthe PAPR level of said transmitted signal, and said steps (b), (e), and(f) are performed during said PAPR reduction procedure.
 19. An apparatusfor protecting and transmitting the side information related topeak-to-average power ratio (PAPR) reduction in a multicarrier system,comprising: a multicarrier modulator for modulating data onto multiplesub-carriers and generating a data modulated signal, wherein saidmulticarrier modulator comprises a PAPR reduction device to reduce thePAPR level of said data modulated signal and reserves a plurality ofsub-carriers for protecting and transmitting said side information; aside information coding and modulation device for coding and modulatingsaid side information onto said plurality of sub-carriers and generatinga side information modulated signal; a composer for composing said datamodulated signal and said side information modulated signal, andgenerating a transmitted signal; and a parameter control device for PAPRreduction for determining said side information according to the PAPRlevel of said data modulated signal.
 20. The apparatus for protectingand transmitting the side information related to PAPR reduction in amulticarrier system as claimed in claim 19, wherein said parametercontrol device for PAPR reduction generates PAPR reduction parameters,and said PAPR reduction parameters are said side information.
 21. Theapparatus for protecting and transmitting the side information relatedto PAPR reduction in a multicarrier system as claimed in claim 20,wherein said multicarrier modulator generates said data modulated signalaccording to said PAPR reduction parameters and feedback to saidparameter control device for PAPR reduction.
 22. The apparatus forprotecting and transmitting the side information related to PAPRreduction in a multicarrier system as claimed in claim 19, wherein saidparameter control device for PAPR reduction determines said PAPRreduction parameters according to a PAPR reduction procedure, then saidside information coding and modulation device refers to said PAPRreduction parameters as said side information for coding and modulatingsaid side information onto said plurality of sub-carriers.
 23. Theapparatus for protecting and transmitting the side information relatedto PAPR reduction in a multicarrier system as claimed in claim 19,wherein said parameter control device for PAPR reduction determines saidPAPR reduction parameters after phase optimization, and sends said PAPRreduction parameters to said side information coding and modulationdevice.
 24. The apparatus for protecting and transmitting the sideinformation related to PAPR reduction in a multicarrier system asclaimed in claim 23, wherein said parameter control device for PAPRreduction comprises a phase mapper and a phase optimization unit, andsaid phase mapper provides said PAPR reduction parameters for saidmulticarrier modulator.
 25. The apparatus for protecting andtransmitting the side information related to PAPR reduction in amulticarrier system as claimed in claim 24, wherein said phase mapper isimplemented by an encoder and an M-ary phase-shift keying (PSK) mapper,and said encoder is followed by said M-ary PSK mapper and proceeds theerror-correction coding of said PAPR reduction parameters.
 26. Theapparatus for protecting and transmitting the side information relatedto PAPR reduction in a multicarrier system as claimed in claim 25, saidside information coding and modulation device further comprising: aparity-bit generator for coding the output from said encoder andgenerating an encoded codeword; a symbol mapper for mapping the encodedcodeword from said parity-bit generator to a corresponding sequence; anda partial N-point Inverse Fast Fourier Transform (N-IFFT) for performingthe modulation of N-IFFT according to the frequency arrangement of saidcorresponding sequence and generating said side information modulatedsignal.
 27. The apparatus for protecting and transmitting the sideinformation related to PAPR reduction in a multicarrier system asclaimed in claim 19, said side information coding and modulation devicefurther comprising: an encoder for coding said side information fromsaid phase optimization unit and generating an encoded codeword; asymbol mapper for mapping the encoded codeword from said encoder to acorresponding sequence; and a partial N-point Inverse Fast FourierTransform (N-IFFT) for performing the modulation of N-IFFT according tothe frequency arrangement of said corresponding sequence and generatingsaid side information modulated signal.
 28. An apparatus for protectingand transmitting the side information related to peak-to-average powerratio (PAPR) reduction in a multicarrier system, comprising: amulticarrier modulator for modulating data onto multiple sub-carriersand generating a data modulated signal, wherein said multicarriermodulator comprises a PAPR reduction device to reduce the PAPR level ofsaid data modulated signal and reserves a plurality of sub-carriers forprotecting and transmitting said side information; a side informationcoding and modulation device for coding and modulating said sideinformation onto said plurality of sub-carriers and generating a sideinformation modulated signal; a composer for composing said datamodulated signal and said side information modulated signal, andgenerating a transmitted signal; and a parameter control device for PAPRreduction for determining said side information according to the PAPRlevel of said transmitted signal.
 29. The apparatus for protecting andtransmitting the side information related to PAPR reduction in amulticarrier system as claimed in claim 28, wherein said parametercontrol device for PAPR reduction generates PAPR reduction parameters,and said PAPR reduction parameters are said side information.
 30. Theapparatus for protecting and transmitting the side information relatedto PAPR reduction in a multicarrier system as claimed in claim 29,wherein said multicarrier modulator generates said data modulated signalaccording to said PAPR reduction parameters.
 31. The apparatus forprotecting and transmitting the side information related to PAPRreduction in a multicarrier system as claimed in claim 28, wherein saidparameter control device for PAPR reduction determines said PAPRreduction parameters according to a PAPR reduction procedure, and duringthat time, said side information coding and modulation device refers tosaid PAPR reduction parameters as said side information for coding andmodulating said side information onto said plurality of sub-carriers.32. The apparatus for protecting and transmitting the side informationrelated to PAPR reduction in a multicarrier system as claimed in claim28, wherein said parameter control device for PAPR reduction selectssaid PAPR reduction parameters during phase optimization, and sends saidPAPR reduction parameters to said side information coding and modulationdevice.
 33. The apparatus for protecting and transmitting the sideinformation related to PAPR reduction in a multicarrier system asclaimed in claim 32, wherein said parameter control device for PAPRreduction comprises a phase mapper and a phase optimization unit, andsaid phase mapper provides said PAPR reduction parameters for saidmulticarrier modulator.
 34. The apparatus for protecting andtransmitting the side information related to PAPR reduction in amulticarrier system as claimed in claim 33, wherein said phase mapper isimplemented by an encoder and an M-ary phase shift keying (PSK) mapper,and said encoder is followed by said M-ary PSK mapper and proceeds theerror-correction coding of said PAPR reduction parameters.
 35. Theapparatus for protecting and transmitting the side information relatedto PAPR reduction in a multicarrier system as claimed in claim 33, saidside information coding and modulation device further comprising: aparity-bit generator for coding the output from said encoder andgenerating an encoded codeword; a symbol mapper for mapping the encodedcodeword from said parity-bit generator to a corresponding sequence; anda partial N-point Inverse Fast Fourier Transform (N-IFFT) for performingthe modulation of N-IFFT according to the frequency arrangement of saidcorresponding sequence and generating said side information modulatedsignal.
 36. The apparatus for protecting and transmitting the sideinformation related to PAPR reduction in a multicarrier system asclaimed in claim 28, said side information coding and modulation devicefurther comprising: an encoder for coding said side information fromsaid phase optimization unit and generating an encoded codeword; asymbol mapper for mapping the encoded codeword from said encoder to acorresponding sequence; and a partial N-point Inverse Fast FourierTransform (N-IFFT) for performing the modulation of N-IFFT according tothe frequency arrangement of said corresponding sequence and generatingsaid side information modulated signal.